Switching elements, such as MOSFETs, configuring a drive circuit such as an inverter circuit generate heat when switching of the elements is controlled. Free wheel diodes are connected in parallel to the switching elements respectively. Each free wheel diode also generates heat when a reflux current flows therethrough. Various techniques have been proposed which are directed to equalizing heat balance between the switching element and the free wheel diode.
Inverter circuits often employ an air-cooled or water-cooled cooling structure for the purpose of suppressing heat generation. However, since space is limited in a peripheral area of the inverter circuit, not all the switching elements can be cooled uniformly with the result of difference in heat generation between the upper and lower switching elements. However, no related art has provided means to cope with the above-described problem.